Methods, algorithms, software, circuits, receivers and systems for decoding convolutional code

ABSTRACT

Methods, software, circuits and systems involving a low complexity, tailbiting decoder. In various embodiments, the method relates to concatenating an initial and/or terminal subblock of the serial data block and outputting decoded data from an internal block of the modified data block. The circuitry generally includes a buffer, logic configured to concatenate an initial and/or terminal subblock to the serial data block, and a decoder configured to decode the data block, estimate starting and ending states for the data block, and output an internal portion of the serial data block and the one or more sequences as decoded data. The invention advantageously reduces the complexity of a suboptimal convolutional decoder, ensures smooth transitions at the beginning and end of the serial data block during decoding, and increases the reliability of the starting and ending states, without adding overhead to the transmitted data block.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/330,260, filed Dec. 8, 2008 (currently pending), which is adivisional of U.S. patent application Ser. No. 11/051,789, filed Feb. 4,2005, now U.S. Pat. No. 7,478,314, which claims the benefit of U.S.Provisional Application Nos. 60/599,102 and 60/599,105, filed Aug. 4,2004 and Aug. 5, 2004, respectively, which are incorporated herein byreference in their entireties.

FIELD OF THE INVENTION

The present invention generally relates to the field of encoding anddecoding information. More specifically, embodiments of the presentinvention pertain to methods, algorithms, software, circuits, andsystems for data communications in a wireless network using a lowcomplexity, tailbiting Viterbi decoder.

DISCUSSION OF THE BACKGROUND

In data communications, a tailbiting trellis may be used to reduceoverhead in convolutional codes that may be caused by returning thetrellis to a known ending state. Terminating the encoded data with aknown ending state ensures that the traceback to determine the outputbits is started from the correct state with the correct cost value. Theperformance of the decoder generally degrades if the starting and endingstates are unknown. However, a known ending state requires extraoverhead since known bits need to be added to the transmitted signal toforce the encoder to the known ending state. Tailbiting is a techniquethat forces the starting state to be the same as the ending state,without the penalty of the overhead bits.

In a tailbiting convolutional code, the input bits are generally groupedinto blocks with a fixed block length. For each fixed length block ofbits, the convolutional encoder is initialized with the final data bitsof the code block. Thus, at the end of the block, the encoder is at thesame state as the beginning of the block. However, the convolutionaldecoder in the receiver does not know the starting-and-ending state.

FIG. 1 shows an example of an encoder 10 with a code block length of Nand a convolutional code rate of M/N, with a memory length of k. Inputdata bits x₁x₂ . . . x_(N) are convolutionally encoded by encoder 10 toproduce coded data y₁y₂ . . . y_(M). At any given time, encoder 10 has astate s₁s₂ . . . s_(k). After encoding bit x_(N), s₁s₂ . . . s_(k) willrepresent the ending state of the encoded data block.

Since the beginning-and-ending state of coded data y₁y₂ . . . y_(M) isunknown, decoding the convolutional code is more complicated. However,there will be a signal-to-noise gain since there is no rate loss penaltycompared to a conventional convolutional code that forces the endingstate (i.e., the “tail”) to a known state. In addition, all of the bitsare protected equally, unlike the code with a known tail.

Generally, the optimum method for decoding tailbiting codes is to searchthrough all possible trellis paths with the same initial and endingstate, and choose the trellis path with the lowest cost or lowest metric(i.e., the most likely path). The initial state can be forced to aparticular value by disallowing transitions from other states (e.g., inaccordance with certain predetermined constraints), and the ending statecan be forced to the same value as the initial state by starting thetraceback from the state with the same value. This optimum decodingbecomes prohibitively complex when a convolutional code with many statesis used, as in IEEE Standards 802.11a, 802.1.1b, 802.11g, 802.11n,802.16 and 802.20.

By exploiting the cyclic nature of the tailbiting code, a suboptimaldecoding scheme with smaller decoding complexity can be used fordecoding the convolutional codes. A received block of signals may bereplicated, and one or more replicas may be concatenated with thereceived block and then decoded using a regular Viterbi algorithm(“Viterbi decoding”). Ideally, in such a scheme, the output bits repeatthemselves with a period equal to the block length after a few cycles ofViterbi decoding. However, this convergence may not always happen, andas a result, the algorithm is suboptimal.

To prevent Viterbi decoding from entering into an infinite loop when thealgorithm does not converge, a fixed number of cyclic concatenations maybe decoded, and the output bits at the end used as an estimate of thetransmitted bits (see, e.g., R. V. Cox, C. E. W. Sundberg, “An efficientadaptive circular Viterbi algorithm for decoding generalized tailbitingconvolutional codes,” IEEE Transactions on Vehicular Technology, vol.43, iss. 1, Feb. 1994, pgs. 57-68). However, in this approach, theentire block of received signals is stored until the block is decoded.In a simplified alternative method, the stored code word is decodedtwice, the output from the first decoding cycle is ignored, and theoutput from the second decoding cycle is retained as the decoded output(see, e.g., C. R. Cahn, “Viterbi Decoding with Tail Biting in the IEEE802.16 Standard,” IEEE 802.16 Broadband Wireless Access Working Group,Aug. 15, 2001). Although the additional storage requirement of theaforementioned method can be satisfied in some cases by sharing memoryfrom a deinterleaver (e.g., as is used in IEEE 802.11- and802.16-compliant receivers), these approaches generally require morememory than conventional convolutional codes using an optimal decodingsolution. In addition, due to the multiple decoding cycles, the Viterbidecoder 20, shown in FIG. 2, has to operate at a speed that is amultiple of the data rate.

A need therefore exists to simplify the operation of Viterbi decodersfurther, and without sacrificing performance and/or operationalefficiencies, to keep up with ever-increasing demands for increasednetwork speeds, performance and capabilities.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate to circuitry, systems,methods, algorithms and software for processing and/or determining avalue for a serial data block in a wireless network using a lowcomplexity, tailbiting Viterbi decoder. The method generally includesconcatenating one or more sequences of said serial data block to saidserial data block to generate a decodable data block; decoding saiddecodable data block to estimate a starting and ending state anddetermine a most likely sequence for said serial data block; andoutputting an internal portion of said decodable data block. In a firstembodiment, the method relates to appending and prepending sequences(e.g., initial and terminal subblocks) from the serial data block to theserial data block. A second embodiment relates to sequentially decodingthe serial data block a plurality of times and outputting an internalblock of the decoded data. A third embodiment relates to appending aninitial subblock or prepending a terminal subblock of the serial datablock, then outputting decoded data from an internal block of themodified data block. The algorithms and software are generallyconfigured to implement one or more of the embodiments of the presentmethod and/or any process or sequence of steps embodying the inventiveconcepts described herein.

The circuitry generally comprises (a) a buffer configured to receive aserial data block; (b) logic configured to concatenate one or moresequences of the serial data block to the serial data block; and (c) adecoder configured to (i) decode the serial data block and said one ormore sequences, (ii) estimate a starting and ending state for the serialdata block, and (iii) output an internal portion of said serial datablock and said one or more sequences as decoded data. The systems (e.g.,a receiver, transceiver, or wireless network) generally include acircuit embodying one or more of the inventive concepts disclosedherein.

The present invention advantageously reduces the complexity of asuboptimal convolutional decoder, ensures smooth (or continuous) statetransitions at the beginning and end of the serial data block duringdecoding, and increases the reliability of the starting and endingstates, without adding any overhead to the transmitted data block. Ingeneral, relative to the conventional approaches discussed above, forthe same performance (e.g., number of decoding repetitions), theinventive approach generally provides greater reliability.Alternatively, for the same reliability, the inventive approachgenerally processes less data. These and other advantages of the presentinvention will become readily apparent from the detailed description ofpreferred embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a conventional encoder configured to ensurethat an ending state for a block of convolutional code is the same asits starting state.

FIG. 2 is a diagram showing a decoder configured to determine whether anending state for a block of convolutional code is the same as itsstarting state.

FIG. 3 is a diagram showing a preferred implementation of the presentinvention, in which an initial subblock is appended and a terminalsubblock is prepended to a serial data block.

FIG. 4 is a diagram showing an alternative implementation of the presentinvention, in which a serial data block is decoded three times and themiddle data block is output.

FIG. 5 is a diagram showing another alternative implementation of thepresent invention, in which an initial subblock is appended to a serialdata block and the decoded data is output from a location internal tothe data block.

FIGS. 6A-6C show a modified serial data block useful for explaining ageneral operation of the alternative implementation of FIG. 5.

FIG. 7 is a diagram showing a further alternative implementation of thepresent invention, in which the entire serial data block is appended toitself (e.g., it is decoded twice), and the decoded data is output fromthe middle of the data block.

FIG. 8 is a plot of the error rate as a function of signal-to-noiseratio (SNR) for a decoding technique according to the present inventionand a conventional decoding technique using zero padding for convolutioncode blocks having starting and ending states of the same length.

FIG. 9 is a comparison of the results provided by variousimplementations embodying the present invention.

FIG. 10 is a block diagram of an exemplary decoder according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, and circuits have not been described indetail so as not to unnecessarily obscure aspects of the presentinvention.

Some portions of the detailed descriptions that follow are presented interms of processes, procedures, logic blocks, functional blocks,processing, and other symbolic representations of operations on databits, data streams or waveforms within a computer, processor, controllerand/or memory. These descriptions and representations are generally usedby those skilled in the data processing arts to convey effectively thesubstance of their work to others skilled in the art. A process,procedure, logic block, function, operation, etc., is herein, and isgenerally, considered to be a self-consistent sequence of steps orinstructions leading to a desired and/or expected result. The stepsgenerally include physical manipulations of physical quantities.Usually, though not necessarily, these quantities take the form ofelectrical, magnetic, optical, or quantum signals capable of beingstored, transferred, combined, compared, and otherwise manipulated in acomputer, data processing system, or logic circuit. It has provenconvenient at times, principally for reasons of common usage, to referto these signals as bits, waves, waveforms, streams, values, elements,symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare associated with the appropriate physical quantities and are merelyconvenient labels applied to these quantities. Unless specificallystated otherwise and/or as is apparent from the following discussions,it is appreciated that throughout the present application, discussionsutilizing terms such as “processing,” “operating,” “computing,”“calculating,” “determining,” or the like, refer to the action andprocesses of a computer, data processing system, logic circuit orsimilar processing device (e.g., an electrical, optical, or quantumcomputing or processing device), that manipulates and transforms datarepresented as physical (e.g., electronic) quantities. The terms referto actions, operations and/or processes of the processing devices thatmanipulate or transform physical quantities within the component(s) of asystem or architecture (e.g., registers, memories, other suchinformation storage, transmission or display devices, etc.) into otherdata similarly represented as physical quantities within othercomponents of the same or a different system or architecture.

Furthermore, for the sake of convenience and simplicity, the terms“clock,” “time,” “rate,” “period” and “frequency” are sometimes usedinterchangeably herein, but are generally given their art-recognizedmeanings. Also, for convenience and simplicity, the terms “data,” “datastream,” “waveform” and “information” may be used interchangeably, asmay the terms “connected to,” “coupled with,” “coupled to,” and “incommunication with” (which terms also refer to direct and/or indirectrelationships between the connected, coupled and/or communicationelements unless the context of the term's use unambiguously indicatesotherwise), but these terms are also generally given theirart-recognized meanings.

The present invention concerns methods, algorithms, software, circuitry,and systems for processing (and/or determining a value for) a serialdata block using a low complexity, tailbiting Viterbi decoder. Themethod generally includes concatenating one or more sequences of saidserial data block to said serial data block to generate a decodable datablock; decoding said decodable data block to estimate a starting andending state and determine a most likely sequence for said serial datablock; and outputting an internal portion of said decodable data block.In a first embodiment, the method relates to appending and prependingsequences (e.g., initial and terminal subblocks) from the serial datablock to the serial data block; a second embodiment relates tosequentially decoding the serial data block a plurality of times andoutputting an internal block of the decoded data; and a third embodimentrelates to appending an initial subblock or prepending a terminalsubblock of the serial data block, then outputting decoded data from aninternal block of the modified data block. The algorithms and/orsoftware are generally configured to implement one or more of theembodiments of the present method and/or any process or sequence ofsteps embodying the inventive concepts described herein, although theterm “algorithm” in this context is meant in a general sense (e.g., alogical sequence of steps taken to perform one or more mathematicaland/or computational processes and/or operations), rather than a morespecific, technical sense (such as “Viterbi algorithm,” discussedbelow).

The circuitry generally comprises (a) a buffer configured to receive theserial data block; (b) logic configured to concatenate one or moresequences to the serial data block; and (c) a decoder configured to (i)decode the serial data block and said one or more sequences, (ii)estimate a starting and ending state for the serial data block, and(iii) Output an internal portion of said serial data block and said oneor more sequences as decoded data. The systems (e.g., a receiver,transceiver, or wireless network) generally include a circuit embodyingone or more of the inventive concepts disclosed herein.

The present invention advantageously reduces the complexity of asuboptimal convolutional decoder, ensures smooth transitions at thebeginning and end of the serial data block during decoding, andincreases the reliability of the starting and ending states, withoutadding any overhead to the transmitted data block. In general, relativeto the conventional approaches discussed above, for the same performance(e.g., number of decoding repetitions), the inventive approach generallyprovides greater reliability. Alternatively, for the same reliability,the inventive approach generally decodes less data, thereby (directly orindirectly) improving performance. The invention, in its variousaspects, will be explained in greater detail below with regard toexemplary embodiments.

Exemplary Methods

The present invention relates to methods of processing and/ordetermining a value for a serial data block. A first embodiment relatesto appending and prepending subblocks of the serial data block to theserial data block. A second embodiment relates to sequentially decodingthe serial data block a number of times (e.g. 2 or 3 times) andoutputting an internal block of the decoded data. A third embodimentrelates to appending an initial subblock or prepending a terminalsubblock of the serial data block (e.g., to create or make a modifieddata block), then outputting decoded data from an internal block of themodified data block (e.g., from a first point at least a traceback depthinto the modified data block, to a point at least a traceback depth fromthe end of the modified data block). Each of these embodiments isintended to further reduce the complexity of a suboptimal convolutionaldecoder, ensure smooth transitions at the beginning and end of theserial data block during decoding, and increase the reliability of thestarting and ending states, without adding any overhead to thetransmitted data block.

Prepending and Appending Subblocks to the Serial Data Block

The present invention relates to methods of processing and/ordetermining a value for a serial data block. In a first embodiment, themethod may comprise the steps of (a) appending an initial subblock ofthe serial data block to the serial data block; (b) prepending aterminal subblock of the serial data block to the serial data block; and(c) decoding the prepended terminal subblock, the serial data block, andthe appended initial subblock to estimate a starting state, an endingstate and a most likely sequence for the serial data block. Appending aninitial subblock and prepending a terminal subblock to the serial datablock reduces the complexity of the decoder and ensures smooth and/orcontinuous transitions at the beginning and end of the serial data blockduring decoding, without reducing or adversely affecting the reliabilityof the starting and ending state(s) or adding any overhead to the datablock transmission. It is believed that the smooth decoding transitionsresult from the code trellis being in a steady state at the time of thetransitions from the end of the prepended terminal subblock to thebeginning of the serial data block and from the end of the serial datablock to the beginning of the appended initial subblock.

The term “data block” generally refers to a data sequence of fixedand/or known length. Thus, the serial data block processed in thepresent method may have a length N. For example, 80 bits is aconventional fixed block length in certain digital audio standards. Eventhough the present decoding step is suboptimal and has reducedcomplexity relative to those described in the background referencesmentioned above, the present method enjoys particular applicability todecoding data blocks of relatively short length. Thus, in variousimplementations, N is from 32 to 256 bits, 40 to 200 bits, or 60 to 100bits. However, in the present method, the convolutional code may beconcatenated with one or more further convolutional codes (e.g., a “dualk” code) and/or a block code (e.g., a Reed-Solomon or error checkingcode). As a result, the received data block is not necessarily limitedto such short sequences, but the data block being decoded according tothe present invention preferably has a relatively short length.

The length of the initial subblock and the terminal subblock can vary.At one extreme, the entire data block may be prepended and appended.Preferably, each of the initial subblock and the terminal subblock has alength of at least a traceback depth. A “traceback depth” is generallyrelated to, and thus may be selected or determined in a manner dependanton, the memory length or constraint length of the convolutional code.The traceback depth is generally the decoding depth (e.g., in a Viterbidecoder) where paths that start from any state should converge, and istypically further dependent on the code rate, the channel in which thesystem operates, the desired or target decoder performance and theinitial state of the decoder (to the extent it is known). As the memorylength of the convolutional code increases, the number of statesincreases, and the traceback depth increases. For example, in aconventional (d,k) code, k refers to the memory of the code (e.g., themaximum number of previous bits that determine the current state) and drefers to the free distance of the code. In many conventional wirelesscommunications protocols, k is 6. The constraint length of aconvolutional code is generally (k+1) bits. When the convolutional codeis a (d,k) code, the traceback depth is generally larger than k, and maybe as high as 5(k+1) or more bits. Typically, an algorithm adapted totraceback from a minimum state will have a shorter traceback depth thanan algorithm adapted to traceback from an arbitrary state. Thus,generally speaking, the longer the traceback depth, the better thedecoder performance.

The convolutional code may have a constraint length commonly used inwireless applications and/or digital broadcasting (e.g., audio)standards. Also, the requirement that the starting and ending states bethe same is a constraint that exists for all tailbiting codes. However,most if not all convolutional coding schemes and algorithms suitable foruse in or with the present invention are proprietary, and theconstraints associated therewith do not lend themselves well to generalcharacterization. In any case, the convolutional code(s) most suitablefor the present invention typically only encode transitions betweenspecific states. In a variety of applications for which the presentinvention is particularly suited, the convolutional code and theconstraint(s) comply with a wireless data transmission protocol and/ordigital broadcasting standard, such as IEEE Standard 802.11a, 802.11b,802.11g, 802.11n, 802.16 and/or 802.20. Thus, the method may furthercomprise the step of receiving the fixed-length, serial data block.Also, the code may comprise nearly any cyclic code, such asconvolutional codes and trellis codes.

As will be explained in greater detail below, the present decoding steppreferably comprises Viterbi decoding (or detecting a sequence for) theprepended terminal subblock, the serial data block, and the appendedinitial subblock. Viterbi decoding efficiently determines which sequencefrom among all possible sequences has the highest likelihood of beingthe received sequence. Viterbi decoding the prepended terminal subblockimproves, or contributes to improving, the estimate of the startingstate. Viterbi decoding the appended initial subblock estimates ordetermines a value for the ending state. When the prepended terminalsubblock has a length of at least a traceback depth, Viterbi decodingshould converge by the time the end of the prepended terminal subblockis reached.

Given the constraint on all tailbiting encoded bitstreams (or datablocks) that the starting and ending states are the same, when thestarting state and the ending state are not the same, this is a goodindication of an error (e.g., in the transmitted sequence). Thus, theinvention may be useful in applications for which tailbiting codes areused, such as wired modems, and the method may further comprise thestep(s) of comparing the estimated starting state and the estimatedending state, and optionally, indicating an error if the estimatedstarting state and the estimated ending state are not identical.

An Exemplary Simplified Tailbiting Trellis Decoding Scheme

As stated above, one exemplary aspect of the invention relates to a lowcomplexity tailbiting Viterbi decoder and methods for processingconvolutional code blocks using the inventive decoder. In the presentinvention, the goal is to obtain the most likely (or “maximumlikelihood”) sequence in a block of data that is encoded using atailbiting code in a relatively low-complexity Viterbi decoder, areliable starting and ending state, and/or an indication of thereliability of the decoded sequence by comparing the estimate of thestarting and ending state (e.g., comparing the starting state estimateand the ending state estimate to each other). At a certain tracebackdepth (denoted as “L”), the Viterbi algorithm has a reasonablelikelihood of convergence. Although convergence is not guaranteed at anyparticular traceback depth, in most applications, a particular orpredetermined traceback depth will lead to good sequence error rate at areasonable latency.

FIG. 3 shows an exemplary “circularized” code block 100 for use in thepresent invention. Circularized code block 100 comprises an encoded,received block 110 (in turn, comprising initial sequence 112 a, datasequence 116 and terminal sequence 114 a), a prepended sequence 114 band an appended sequence 112 b. As shown by arrow 130, terminal sequence114 a may be copied and prepended to the beginning of encoded block 110,and as shown by arrow 140, initial sequence 112 a may be copied andappended to the end of encoded block 110. As a result, if the length ofinitial sequence 112 a (and thus, of appended sequence 112 b) is equalto or greater than the traceback depth, after tracing back to the end ofencoded block 110, the state will generally be the same as the statewhen tracing back to the beginning of encoded block 110. If the state isnot the same, an error has occurred. On the other hand, if the state isthe same, it is not necessarily true (but it very likely) that no erroroccurred. Although the tailbiting encoder encodes the same starting andending state, after decoding, the states may not necessarily be the samebecause the state at the beginning of encoded block 110 is determinedusing prepended sequence 114 b and at least a portion of initialsequence 112 a, whereas the state at the end of encoded block 110 isdetermined using terminal sequence 114 a, a portion of data sequence 116and at least a portion of appended sequence 112 b. However, if decodingis correct, the states will be the same, and an error will generally notbe indicated. This may be more easily understood with reference to amore specific example.

If initial sequence 112 a consists of a sequence z₁ . . . z_(k) andterminal sequence 114 a consists of a sequence z_(N−L+1) . . . z_(N),then appended sequence 112 b will generally consist of the sequence z₁ .. . z_(k) and prepended sequence 114 b will generally consist of thesequence z_(N−L+1) . . . z_(N). Circularly combining these blocks asshown in FIG. 3 and as described above leads to a “circularized” codeblock 100 having continuous state transitions at the beginning and endof received block 110. Generally, in this first embodiment, the initialsequence consists of a subblock of the first L bits of the data block,and the terminal sequence consists of a subblock of the last L bits ofthe data block, where the traceback depth ≦L.

Such circular prepending and appending of encoded creates a smooth orcontinuous state transition at the edges of the original code block 110,and can effectively increase the efficiency and/or channel capacity ofthe code by enabling elimination of the conventional “knownstarting/ending state” overhead bits. Alternatively, the inventionenables decreasing the traceback depth without increasing theconventional “known starting/ending state” overhead penalty.

Viterbi decoding generally starts from the beginning of the circularizedcode block 100 (e.g., bit z_(N−L+1) of prepended sequence 114 b) andstops at the end of the circularized code block 100 (e.g., bit z_(k) ofappended sequence 112 b). Initially, Viterbi decoding may be conductedwith an equal metric for all states. However, the decoder generally doesnot output the bits from the prepended sequence 114 b or the appendedsequence 112 b, as will be explained below with regard to the presentcircuitry.

The prepended sequence 114 b, generally contributes to obtaining areliable estimate of the starting state of original code block 110, andthe appended sequence 112 b generally ensures that the ending state oforiginal code block 110 is reliable. Although the reliability of thestarting state and ending state estimates is generally better thanconventional decoding methods, there may be error patterns that cause amismatch in the starting state and the ending state in the presentinvention. In general, the occurrence of such a mismatch indicates asequence detection error. In one embodiment, a sequence detection errorindication can be passed to the sequence detection algorithm downstreamfrom the Viterbi decoder. Alternatively, the Viterbi algorithm can bere-run with this error information (for example, by biasing the weightsto favor one or more starting states other than the decoded startingstate). A fixed or predetermined number of retries may be conventionallyset (e.g., by a counter) to place a bound or limit on the decoding time.

The present invention is not limited to the prepended/appended sequenceexample given above, which merely illustrates the present decodingmethod and algorithm. A receiver comprising the present decoder maydecode from the beginning of a data frame, similar to conventionalapproaches (see, e.g., C. R. Calm, “Viterbi Decoding with Tail Biting inthe IEEE 802.16 Standard,” IEEE 802.16 Broadband Wireless Access WorkingGroup, Aug. 15, 2001). For example, after decoding the data frame twice(e.g., using decoding stages 0 to [2N−1], where N is the frame size),the output bits corresponding to the middle decoding stages (e.g., N/2to [3N/2]−1) comprise the decoded bits. This approach contrasts withthat of conventional methodology (e.g., Cahn, above), where the outputcorresponding to the decoding stages N to 2N−1 is used. In our case, aslong as N/2>L, reliable decoded bits can be obtained.

The increase in complexity for the present scheme relates to theoperations associated with Viterbi decoding the bits of the prependedand appended code sequences. However, if an alternate method (such asthose discussed in the Discussion of the Background above) is used tofurther improve the error rates, the increase in complexity is amultiple of this complexity. The average increase in complexity in thepresent scheme might be less than 2 times, but the decoding hardware hasto design for the worst case. Normally, a single cycle of Viterbidecoding for the circularized code block is sufficient to obtaincommercially acceptable bit error rate performance.

Sequentially Decoding the Serial Data Block and Outputting an InternalData Block

In a second embodiment, the present method determines a value for aserial data block, and comprises the steps of: (1) decoding the serialdata block at least three times; and (2) outputting an internal decodedserial data block as the value for the serial data block. As for thefirst embodiment above, the serial data block comprises a cyclic orconvolutional code and generally has a fixed length N (or, as shown inFIG. 4, M), where N (or M) may be an integer of, for example, from 32 to256 bits. The cyclic or convolutional code typically comprises at leastone constraint, which (together with the tailbiting constraint) maycomply with a digital audio broadcasting protocol or a wireless datatransmission protocol such as IEEE Standard 802.11a, 802.11b, 802.11g,802.11n, 802.16 and/or 802.20. In addition, the method may furthercomprise (i) receiving the serial data block and/or (ii) comparing theestimated starting state and the determined ending state, andoptionally, indicating an error if the estimated starting state and theestimated ending state are not identical.

As for the first embodiment above, Viterbi decoding is a preferredtechnique for processing serial data blocks in this second embodiment.For example, the present decoding step(s) and/or starting/ending stateestimating and/or determining steps may comprise Viterbi decoding theserial data block. However, in this preferred case, the serial datablock is generally Viterbi decoded at least three successive times.Consistent with the inventive approach, an internal decoded serial datablock (e.g., a Viterbi decoded block other than the first or lastViterbi decoded block, such as the second Viterbi decoded block) isgenerally output as the value for the serial data block.

FIG. 4 slims an exemplary serial data block configuration 200 forprocessing convolutional code according to this second embodiment,generally comprising first (or “prepended”) code block 210, serial datablock 220 (to be decoded and output as received serial data), andthird/last (or “appended”) code block 230. Generally, the first codeblock 210 is received and stored in a buffer, and the stored data orcode block is read three successive times to form serial data blockconfiguration 200. Thus, the identity and/or sequence of first codeblock 210, serial data block 220, and last code block 230 are identicalto one another (e.g., all consist of the sequence z₁z₂ . . . z_(M)).This approach further simplifies the trellis decoder, because circuitry(such as pointer logic and/or extra memory) for indicating and/orstoring appended and/or prepended code sequences is not necessary.

As described above for the first embodiment of the present method,Viterbi decoding the first code block 210 and at least part of thesecond block 220 improves, or contributes to improving, the reliabilityof the estimate of the starting state of the data block and/or decodertrellis. Viterbi decoding the last code block provides a continuousstate transition at the end of a data block. Because the identity and/orsequence of first code block 210 and last code block 230 are identical,the starting state and ending state should be the same. Because theserial data block is generally longer than the traceback depth (i.e.,N>L), the decoder trellis will reach a steady state and have a maximumlikelihood for convergence when the serial data block 220 is decoded.Consistent with the inventive approach, the decoded serial data block220 (e.g., the second, internal or middle Viterbi decoded block) isgenerally output as the value for the serial data block. In part becausethe entire data block is effectively prepended and appended (and in partbecause one purpose of the present invention is to simplify the trellisdecoding Scheme), this second embodiment is particularly advantageouswhen the code block is small (e.g., generally less than about 200 bits,or in some cases less than about 100 bits).

Adding an Initial or Terminal. Sequence to the Serial Data Block andOutputting Decoded Data from within the Serial Data Block

In a third embodiment, the present method concatenates an initial orterminal subblock to a serial data block to form or create a modifieddata block, and comprises the steps of: (A) estimating a starting statefollowing (e.g., for the first position after) an initial portion of themodified data block; (B) decoding a remainder of the modified datablock; and (D) outputting the decoded modified data block remainder upto a terminal portion of the modified data block as decoded data. Inthis third embodiment, the initial subblock (which, like the firstembodiment above, is appended to the serial data block) preferablycomprises or consists of the first 2*L bits of the serial data block,and the terminal subblock (which, like the first embodiment above, isprepended to the serial data block) preferably comprises or consists ofthe last 2*L bits of the serial data block, where the traceback depth≦L. However, decoded data is generally output beginning at the first bitposition following an initial portion of the modified data block, wherethe initial portion preferably has a length of at least the tracebackdepth (e.g., L bits as indicated above).

Thus, the initial or terminal subblock (or sequence) added to the serialdata block is longer than the initial portion of the modified data blockto be decoded, generally at least twice the length of the initial orterminal subblock. For example, if the initial portion (to be decodedand/or for estimating the starting state [along with a subsequentportion of the modified data block]) consists of the first P₁ bits ofthe received data block, then the initial subblock generally includes atleast the first P₂ bits of the received data block, where P₂≧2*P₁.

As for the first and second embodiments above, the serial data blockcomprises a cyclic or convolutional code that may have at least oneconstraint that may comply with a wireless data transmission protocoland that may have a fixed length N (or, as shown in FIG. 5, M). Also,the method may further comprise comparing the estimated starting stateand ending state, and optionally, indicating an error if the estimatedstarting and ending state(s) are not identical.

Viterbi decoding is also a preferred aspect of this third embodiment.For example, the step of estimating a starting state for the modifieddata block preferably comprises Viterbi decoding the initial portion andL additional stages (or bits) of the modified data block remainder,where L is the traceback depth (and where L may be P₂-P₁, as set forthtwo paragraphs above). Furthermore, the decoding step may compriseViterbi decoding the modified serial data block remainder (the modifieddata block minus the initial portion) and the remaining appended initialsubblock or prepended terminal subblock. As a result, the method mayfurther comprise the step(s) of (i) determining an ending state usingthe terminal portion of the (decoded) modified data block (where theterminal portion has a length of at least the traceback depth), and/or(ii) reversing the Viterbi decoded modified data block remainder and theViterbi decoded remaining appended initial subblock (or remainingprepended terminal subblock) to provide a Viterbi decoded serial datablock.

FIG. 5 shows a first exemplary serial data block configuration 300 forprocessing convolutional code according to this third embodiment,generally comprising a received serial data block 310 and an appendedinitial code subblock 320. Generally, appended initial subblock 320includes appended initial portion 322, which is identical to initialdata portion 312 (e.g., the first L bits of serial data block 310), andappended initial subblock remainder 324, which is identical to initialdata subblock remainder portion 314 (e.g., the second L bits of serialdata block 310). Like the embodiment(s) described above, serial datablock 310 may be received and stored in a buffer. Serial data block 310and/or modified data block 300 is decoded beginning at bit z₁ in initialportion 312, and decoded data are output beginning at a point in initialsubblock remainder portion 314 or serial data block remainder 316,depending on the traceback depth. For example, if the traceback depthL=P₁, then a decoding decision is made after bit z_(P1+1) has beenprocessed, and decoded data are output beginning at bit positionz_(P1+1) in serial data block remainder 340. The serial data blockremainder 340 is then decoded and output as the value for bit positionsthrough z_(M) of the serial data block. For bit positions z₁ throughZ_(P1), appended initial subblock 320 is decoded, but only initialportion 322 is output as decoded data. Thus, alternatively, appendedinitial subblock remainder 324 may have a length of at least P₂-P₁. Alength of at least a traceback depth is preferred for appended initialsubblock remainder 324.

A more general operation of this embodiment shall be explained withregard to FIGS. 6A-6C. FIGS. 6A-6C each show a general modified serialdata block 300*, having a concatenated initial or terminal subblocktherein. Generally, with reference now to FIG. 6A, path metrics arecomputed for modified serial data block 300*, starting from bit positionA up to bit position D. Decoded data may then be output by tracing backL bits to bit position C, and outputting the data starting at bitposition C. The distance in bits between bit positions A and B, P,generally corresponds to the length P₁ of appended initial portion 322in FIG. 5. Referring back to FIG. 6A, for optimal performance, K and Pare each ≧L, although P or K can be <L (e.g., to decrease theoperational speed of the decoder, but at the expense of optimalperformance; if K<L, then P<L; if P≧L, then. K≧L).

FIG. 6B shows the modified serial data block 300* at the time that thefinal data state (i.e., up to/terminating at bit position E) is output.For best results, the distance K between bit positions E and F should beat least L bits (i.e., K≧L). However, as discussed above, K may besmaller than L. For example, referring to FIG. 6C, at bit position H(one bit from the end of modified serial data block 300*), one tracesback L bits to bit position G and outputs decoded data at that point.However, when K is smaller than L, at the end of modified serial datablock 300* (bit position F), one traces back K bits to bit position E′and outputs all of the decoded bits from bit position G to bit positionE′.

This third approach provides both (i) a reliable estimate, determinationor calculation of the ending state of the data block and/or decodertrellis and (ii) the value for bit positions z₁ through z_(P1) of theserial data block with a continuous state transition at the end of thedecoded data. Thus, consistent with the inventive approach, an internalportion of the (modified) serial data block 300 is decoded and output asthe Viterbi decoded block. However, this third approach generallynecessitates re-ordering the decoded data. Decoded data may bere-ordered (or reversed) by storing the decoder output in a bufferhaving appropriate pointer logic to indicate the correct bit positionsfor the decoded data. When the decoded data are output in parallel(e.g., when the decoder has a parallel downstream interface), there isno latency penalty using this third approach.

This third approach also works for prepending a terminal subblock (whichcomprises a [i] terminal portion that may have a length of at least atraceback depth and [ii] a terminal subblock remainder that may have alength of at least a traceback depth or a decoder memory length) of theserial data block to the serial data block. In such a case, the startingstate is estimated using at least the prepended terminal portion,outputting decoded data starts at the first bit position of the terminalsubblock remainder following the prepended terminal portion and ends atthe last bit position of the terminal portion in the serial data block(when the prepended terminal portion has a length equal to the tracebackdepth), but decoding continues until the end of the serial data block inorder to provide a continuous state transition at the end of the decodeddata.

One further advantage of this approach is that the decoder can generallyoperate on the same sequence as the rest of the receiver circuitry(although the rate/speed will be greater than that of the rest of thereceiver circuitry, generally by a factor of [(M+P₁+P₂)/M]). However,because the data is output from a position inside the received datablock, the data output from the decoder will not be in the same sequenceas the received serial data block 310. Thus, the present method mayfurther comprise the step of re-ordering or rearranging the decodeddata, such that the decoded appended subblock is subsequently read ortransmitted before the decoded remainder of the serial data block.Because this third embodiment can append an initial subblock having alength of about twice the decoder traceback depth (or less), thisembodiment may be advantageous when the code block is slightly largerthan in other embodiments (e.g., from about 60, 80 or 100 bits to about250, 500, or 1000 bits).

FIG. 7 shows a second exemplary serial data block configuration 350 forprocessing convolutional code according to this third embodiment,generally comprising first serial data block 360 and second serial datablock 370. First serial data block 360 generally consists of firstportion 362 and second portion 364, and second serial data block 370generally consists of first portion 372 and second portion 374.Generally, for logical simplicity, the first and second serial datablocks 360-370 are identical to one another, as are first portions 362and 372, and independently, second portions 364 and 374. Like theembodiments) described above, first serial data block 360 may bereceived and stored in a buffer, then read twice to form serial datablock configuration 350. As for the other embodiments of the presentmethod, the internal block or “middle portion” 380 of the data blockconfiguration 350 is decoded and output as the value for the decodedserial data block. However, as for the example of FIG. 5, there is aslight twist as to how the decoded data is output.

In the example of FIG. 7, M is generally an even number. Viterbidecoding part or all of the first serial data block 360 provides areliable estimate of the starting state of the data block 380 and/ordecoder trellis, and Viterbi decoding the second serial data block 370provides a reliable estimate, determination or calculation of the endingstate of the data block and/or decoder trellis. However, the secondportion 364 (e.g., the last M/2 data bits z_((M/2)+1) . . . x_(M/2) offirst serial data block 360) and the first portion 372 (e.g., the firstM/2 data bits z₁z₂ . . . z_(M2) of second serial data block 370) aredecoded and output as the value for the serial data block. Thus,consistent with the inventive approach, the middle portion 380 of thedata block configuration 350 is output as the Viterbi decoded data.Where first and second serial data blocks 360-370 have a length of atleast twice the traceback depth (e.g., M≧2 L), the decoder trellis willreach a steady state and have a maximum likelihood for convergence whenthe “middle portion” 380 of the data block configuration 350 is decoded.

One advantage of this approach is that the decoder can generally operateat a lower multiple than in the approaches of the cited backgroundliterature. Furthermore, although there may be some latency in thedecoder output, this latency is generally lower or reduced relative tothe conventional approaches discussed in the Discussion of theBackground above. Thus, for the same performance (e.g., number ofdecoding repetitions), the inventive approach generally provides greaterreliability; alternatively, for the same reliability, the inventiveapproach generally processes less data. Moreover, because the data maybe output from a well-defined and logically convenient and/oradvantageous position at the mid-point of the serial data block, thelogic for decoding and outputting the received data block may berelatively simple. In addition, the last L states (where L is thetraceback depth) of the serial data block may be decoded more reliablythan the conventional approaches discussed above, because appendedremainder portion(s) 324 (FIG. 5) or 374 (FIG. 7) contribute to theconvergence of the Viterbi decoder at those states.

Results from the Present Tailbiting Trellis Decoding Schemes

To demonstrate the decoding performance of the present scheme, asimulation for a code block length of 192 bits was performed. Thepresent decoding algorithm was compared to an otherwise identicalconvolutional code block, but having a zero padded tail (i.e., in whichthe starting/ending state consisted of six [6] all zero bits) and adecoder configured for known starting and ending states, taking intoaccount the code rate loss. The code block arrangement representative ofthe invention in FIG. 8 used both appended and prepended subblocks, eachhaving a length of 72 bits. The results are shown in FIG. 8, which is agraph 400 depicting the bit error rate (BER) as a function ofsignal-to-noise ratio (“SNR,” defined in this case as E_(b)/N₀) for thetwo decoding schemes.

The results for the present tailbiting convolutional code scheme, usingthe present low complexity decoder (described below), are plotted asline 410. Results for the conventional zero-padded convolutionaldecoding scheme are plotted as line 420. The comparative results showthat the present scheme has performance similar to, or approaching, theconventional zero-padded scheme for the same SNR. The present lowcomplexity decoder is only slightly more complex than a conventionalconvolutional decoder using known starting and ending states, while itis generally significantly simpler than conventional tail-biting Viterbidecoders and algorithms in which the starting and ending states areunknown.

To further reduce the complexity of the present tail-biting Viterbidecoder and method (although at the expense of potential performanceloss), the size of the prepended subblock (denoted as L1) and theappended subblock size (denoted as L2) was reduced to less than half ofthe block size. FIG. 9 shows the performance of various implementationsof the present decoding scheme for a block of data with block lengthN=80 transmitted through a mobile hilly terrain environment and decodedusing the present tail-biting decoder with appended and prependedsubblocks having lengths L1=L2=80 (case 1), lengths L1=L2=36 (case 2),and separately, lengths L1=18 and L2=36 (case 3).

Results 450 for cases 1, 2, and 3 are shown in lines 480, 460, and 470,respectively. Case 1 (representative of the second embodiment above)showed substantially no performance loss relative to decoding 5 times oreven 12 times (lines 490 a-c, which are essentially superimposed on oneanother). The fact that two of the lines 490 a-b, for the cases wherethe code block was decoded 5 times and either the second block (490 b)or the fourth block (490 a) were output as the decoded data, wereessentially superimposed demonstrates that one obtains substantially thesame results as long as an internal (non-terminal) code block isselected for the decoded output. Case 2 showed almost no performanceloss relative to case 1 (about 0.025 dB). Even for the case 3 (whichconfiguration contains only 134 decoding stages), the performance lossis only about −0.05 dB or less relative to case 1, decoding the entireblock three times (which configuration contains 240 decoding stages),thereby demonstrating that prepending and appending relatively shortsequences of the code block does not significantly adversely affectperformance.

Exemplary Software

The present invention also includes algorithms, computer program(s)and/or software, implementable and/or executable in a general purposecomputer or workstation equipped with a conventional digital signalprocessor, configured to perform one or more steps of the method and/orone or more operations of the hardware. Thus, a further aspect of theinvention relates to algorithms and/or software that implement the abovemethod(s). For example, the invention may further relate to a computerprogram, computer-readable medium or waveform containing a set ofinstructions which, when executed by an appropriate processing device(e.g., a signal processing device, such as a microcontroller,microprocessor or DSP device implementing the present Viterbi decoder),is configured to perform the above-described method and/or algorithm.

For example, the computer program may be on any kind of readable medium,and the computer-readable medium may comprise any medium that can beread by a processing device configured to read the medium and executecode stored thereon or therein, such as a floppy disk, CD-ROM, magnetictape, hard disk drive, or ROM (e.g., EPROM, boot ROM or flash memory)and/or RAM (e.g., DRAM, SRAM or pseudo-SRAM). Such code may compriseobject code, source code and/or binary code.

The waveform is generally configured for transmission through anappropriate medium, such as copper wire, a conventional twisted pairwireline, a conventional network cable, a conventional optical datatransmission cable, or even air or a vacuum (e.g., outer space) forwireless signal transmissions. The waveform and/or code for implementingthe present method(s) are generally digital, and are generallyconfigured for processing by a conventional digital data processor(e.g., a microprocessor, microcontroller, or logic circuit such as aprogrammable gate array, programmable logic circuit/device orapplication-specific [integrated] circuit).

In various embodiments, the computer-readable medium or waveformcomprises at least one instruction to (i) Viterbi decode the prependedterminal subblock, the serial data block, and the appended initialsubblock; (ii) compare the estimated starting state and the estimatedending state; and/or (iii) indicate an error if the estimated startingstate and the estimated ending state are not identical.

An Exemplary Circuit

In a further aspect, the present invention relates to a circuit,comprising (a) a buffer configured to receive a serial data block; (b)logic configured to concatenate one or more sequences of the serial datablock to the serial data block; and (c) a decoder configured to (i)decode the serial data block and the one or more sequences, (ii)estimate a starting and ending state for the serial data block, and(iii) output an internal portion of said serial data block and said oneor more sequences as decoded data. The present circuitry is generallyconfigured to implement the present method described above, and thiscircuitry represents a minimum set of circuit elements adapted toperform any of the embodiments of the present method above. Thus, infurther embodiments directed towards implementing one or more of theembodiments of the present method above, the logic may be furtherconfigured to append an initial subblock and/or prepend a terminalsubblock of the serial data block to the serial data block, and thedecoder may be further configured to estimate (1) the starting statefrom at least the prepended terminal subblock and/or (2) the endingstate from at least the appended initial subblock.

In further embodiments, the circuit may further comprise outputcircuitry configured to output the decoded serial data block, and/or thelogic may further comprise pointer logic configured to indicate an endlocation in the buffer for the initial subblock and/or a start locationin the buffer for the terminal subblock. In addition, the logic may befurther configured to instruct the decoder to output (a) a decodedappended initial subblock remainder, then the decoded remainder of theserial data block, or (b) a decoded serial data block portion/remainder,then the prepended terminal subblock remainder, consistent with thethird embodiment of the present method above. In a preferred embodimentof the present circuit, the decoder comprises a Viterbi decoder.Alternatively and/or additionally, the decoder may comprise anestimator.

FIG. 10 shows an exemplary receiver 500, including receiving port 510,buffer 520, decoder 530, decoder logic 540, clock 550 and outputcircuitry 560. Generally, a serial data block DATA is received from achannel into port 510. The channel is preferably a wireless channelthat, for example, is compliant with one or more IEEE standards forwireless communications (e.g., 802.11a, 802.11b, 802.11g, 802.11n,802.16 and/or 802.20). Port 510 is a conventional (and in oneembodiment, wireless) receiving port that may have an antennacommunicatively coupled thereto and that is configured to receive analogor digital data DATA (e.g., encoded sequence z₁z₂ . . . z_(M) with[Gaussian] channel noise added thereto; see, e.g., FIG. 2). In the caseof analog data, port 510 may comprise conventional sampling and bufferand/or amplifier circuitry. In the case of digital data, port 510 maycomprise latch and/or amplifier circuitry. It is well within theabilities of one skilled in the art to design and use such portcircuitry.

Buffer 520 generally comprises a memory array configured to store one ormore serial data blocks, and may comprise a conventionalfirst-in-first-out (FIFO) buffer, a simplex dual port memory with one ormore pointers adapted to identify predetermined bit locations (e.g., theend of the initial subblock, the beginning of the terminal subblock, themidpoint of the serial data block, etc.), one or more shift registers(and if more than one, having a demultiplexer in communication withinputs thereof configured to store part or all of a serial data block ina particular shift register and a multiplexer in communication withoutputs thereof configured to select part or all of a serial data blockin a particular shift register for outputting to decoder 530), etc. Inone implementation, buffer 520 comprises an embedded memory.

Decoder 530 typically comprises a Viterbi decoder, configured to decodethe serial data block and estimate a starting state and an ending statefor the serial data block, generally using a conventional Viterbialgorithm (which may be implemented in hardware and/or software, buttypically, in hardware). Thus, the decoder in the present circuit may beadapted for (i) hard decisions or soft decisions, (ii) punctured code ornon-punctured code, and/or (iii) concatenated code (e.g., aconvolutional code block concatenated with a block code sequence and/ora second convolutional code block, as described above). Decoder 530 maybe further adapted to process code at a conventional rate of k/n, wheren>k (or, consistent with the above description, N/M or N/M). Also, whendecoder 530 comprises a Viterbi decoder, the Viterbi decoder may beconfigured to eliminate or “prune” branches from the decoder trellisthat correspond to disallowed states (e.g., code containing a datasequence that violates one or more coding constraints).

Decoder logic 540 provides instructions, commands and/or control signalsto the buffer 520 and decoder 530 in receiver 500. Thus, logic 540 maycontrol (i) reading from and writing to buffer 520, (ii) setting orresetting one or more pointers in buffer 520, (iii)decoding/estimating/determining/calculating functions in decoder 530,etc. Reading from and writing to buffer 520 may be controlled byactivation and deactivation of one or more write enable and/or readenable signals, selection of a particular shift register or other memoryelement within buffer 520 for storing or outputting data using a(de)multiplexer, etc. The decoder functions are described elsewhereherein, but the timing of such decoder functions (e.g., when to startand/or stop such functions), as well as reading functions within buffer520 (e.g., reading a particular initial or terminal subblock) may becontrolled by one or more counters in logic 540. In an embodiment ofdecoder 530 adapted for implementing the embodiment of the presentmethod exemplified in FIG. 7, the timing of functions in decoder 530 andcertain reading functions in buffer 520 may be controlled using, e.g.,relatively simple divider logic. It is well within the abilities ofthose skilled in the art to design, implement and use logic configuredto perform such control functions.

Clock 550 receives a reference clock signal (e.g., REF) and provides aperiodic signal having a fixed and/or predetermined frequency to othercircuit blocks in receiver 500. However, the clock or timing signalreceived in decoder 530 may be multiplied by a conventional clockmultiplier before use (as described above). The clock or timing signalreceived in decoder logic 540 may be used by one or more counterstherein (e.g., the counter[s] may count clock cycles to control thestate of one or more control signals generated in logic block 540).

Output circuitry 560 receives decoded data from decoder 530 and providesoutput data DATAOUT (e.g., decoded, noise-affected sequence x₁{circumflex over (x)}₂ . . . {circumflex over (x)}_(N); see FIG. 2).Output circuitry 560 is conventional, and may comprise one or moreconventional amplifiers and one or more conventional output buffer(s)and/or conventional output driver(s).

An Exemplary Receiver, System and Network

A further aspect of the present invention relates to a receiver,comprising the present circuit and (if not already present or required)a receiver port communicatively coupled to the buffer, configured toreceive serial data from a channel. The receiver port is generally asdescribed above with regard to port 510 in the present circuit. In oneimplementation, the present receiver is embodied on a single integratedcircuit.

The receiver may further include a clock circuit configured to provide areference clock signal to the receiver port and the buffer. In furtherembodiments, the receiver may convert serial data from the network toparallel data for a downstream device or circuit, and convert paralleldata from the device (or the same or different circuit) to serial datafor the network.

The present invention relates to a system for transferring data on oracross a network, comprising the present receiver and at least onetransmitter, communicatively coupled to the receiver port of thereceiver, configured to transmit one or more serial data blocks to anexternal receiver. The system may further comprise an encodercommunicatively coupled to the transmitter and configured to generatethe serial data block(s). The encoder, which is largely conventional,generally encodes cyclic or convolutional code, which may be interleavedand/or concatenated with other codes as described herein. The encoder inthe present system is slightly different from encoders that have beenused to generate code having known starting and ending states (e.g.,zero-padded data blocks).

As explained above, the present invention is particularly suited forwireless data communications. Thus, the present system and/or receivermay comply with a digital audio broadcasting protocol or one or moreIEEE Standards for wireless communications (e.g., 802.11a, 802.11b,802.11g, 802.11n, 802.16 and/or 802.20).

A further aspect of the invention concerns a wireless network,comprising (a) a plurality of the present systems, communicativelycoupled to each other; and (b) a plurality of communications devices,wherein each communications device is communicatively coupled to atleast one of the systems. In various embodiments, the network comprisesa wireless network and/or one that is compatible with one or more ofIEEE Standards 802.11a, 802.11b, 802.11g, 802.11n, 802.16 and/or 802.20(preferably one that is compatible with IEEE Standard 802.11a, 802.11gor 802.16), and each of the plurality of information blocks may comprisea standard (digital and/or audio) data block (80 bits long). The networkmay have one or more channels (or characteristic signal-carryingfrequencies or frequency bands), over which the serial data blocks maybe transmitted.

CONCLUSION/SUMMARY

Thus, the present invention generally relates to low-complexitytechniques for decoding information, and more specifically, to methods,algorithms, software, circuits and systems for communicating data in awireless network using a low complexity, tailbiting Viterbi decoder. Thepresent invention advantageously reduces the complexity of a suboptimalconvolutional decoder, ensures smooth transitions at the beginning andend of the serial data block during decoding, and increases thereliability of the starting and ending states, without adding anyoverhead to the transmitted data block.

The method generally includes concatenating one or more sequences of aserial data block to the serial data block to generate a decodable datablock; decoding the decodable data block to estimate a starting andending state and determine a most likely sequence for the serial datablock; and outputting an internal portion of the decodable data block.In a first embodiment, the method relates to appending and prependingsequences (e.g., initial and terminal subblocks) of the serial datablock to the serial data block. A second embodiment relates tosequentially decoding the serial data block a plurality of times andoutputting an internal block of the decoded data. A third embodimentrelates to appending an initial subblock or prepending a terminalsubblock of the serial data block, then outputting decoded data from aninternal block of the modified data block. The algorithms and softwareare generally configured to implement one or more of the embodiments ofthe present method and/or any process or sequence of steps embodying theinventive concepts described herein.

The circuitry generally comprises (a) a buffer configured to receive aserial data block; (b) logic configured to concatenate one or moresequences of the serial data block to the serial data block; and (c) adecoder configured to (i) decode the serial data block and said one ormore sequences, (ii) estimate a starting and ending state for the serialdata block, and (iii) output an internal portion of said serial datablock and said one or more sequences as decoded data. The systems (e.g.,a receiver, transceiver, or wireless network) generally include acircuit embodying one or more of the inventive concepts disclosedherein.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the Claims appended hereto and theirequivalents.

What is claimed is:
 1. A circuit comprising: a buffer configured tostore a serial data block; logic configured to append a sequence of theserial data block to the serial data block; and a decoder configured to:decode portions of the serial data block and the appended sequence;compute a first path metric for the serial data block up to a first bitposition; compute a second path metric for the serial data block up to asecond bit position; trace back from the first bit position to a thirdbit position by a first amount smaller than a size of the appendedsequence; trace back from the second bit position to a fourth bitposition by a second amount greater than the size of the appendedsequence; and output an internal portion of the serial data block andthe sequence from the third bit position to the fourth bit position asdecoded data.
 2. The circuit of claim 1, wherein the logic furthercomprises pointer logic configured to indicate a location in the bufferfor the sequence.
 3. The circuit of claim 1, wherein the decoder isfurther configured to estimate a starting state from at least a part ofa prepended terminal subblock and the computed first path metric.
 4. Thecircuit of claim 1, wherein the decoder comprises a Viterbi decoder. 5.The circuit of claim 1, wherein the decoder comprises an estimator. 6.The circuit of claim 1, wherein the first and second path metrics arecomputed such that starting and ending states have essentially a samevalue.
 7. The circuit of claim 1, further comprising an encodercommunicatively coupled to the buffer and configured to generate theserial data block.
 8. The circuit of claim 1, wherein the circuitcomplies with a digital audio broadcasting protocol or a standardselected from the group consisting of IEEE Standard 802.11a, 802.11b,802.11g, 802.11n, 802.16, and 802.20.
 9. The circuit of claim 1, whereinthe logic is further configured to prepend a terminal sequence of theserial data block to the serial data block.
 10. The circuit of claim 1,wherein the decoder is further configured to estimate an ending statefrom the second path metric.
 11. A method comprising: storing a serialdata block; appending a sequence of the serial data block to the serialdata block; decoding portions of the serial data block and the appendedsequence; computing a first path metric for the serial data block up toa first bit position; computing a second path metric for the serial datablock up to a second bit position; tracing back from the first bitposition to a third bit position by a first amount smaller than a sizeof the appended sequence; tracing back from the second bit position to afourth bit position by a second amount greater than the size of theappended sequence; and outputting an internal portion of the serial datablock and the sequence from the third bit position to the fourth bitposition as decoded data.
 12. The method of claim 11 further comprisingindicating a location in the buffer for the sequence.
 13. The method ofclaim 11 further comprising estimating a starting state from at least apart of a prepended terminal subblock and the computed first pathmetric.
 14. The method of claim 11, wherein the decoder comprises aViterbi decoder.
 15. The method of claim 11, wherein the decodercomprises an estimator.
 16. The method of claim 11, wherein the firstand second path metrics are computed such that starting and endingstates have essentially a same value.
 17. The method of claim 11 furthercomprising generating the serial data block.
 18. The method of claim 11,wherein the circuit complies with a digital audio broadcasting protocolor a standard selected from the group consisting of IEEE Standard802.11a, 802.11b, 802.11g, 802.11n, 802.16, and 802.20.
 19. The methodof claim 11 further comprising prepending a terminal sequence of theserial data block to the serial data block.
 20. The method of claim 11further comprising estimating an ending state from the second pathmetric.